[Doc] Clarify CosyVoice3 lazy graph latency and memory headroom

Signed-off-by: Sy03 <1370724210@qq.com>

vllm_omni/deploy/cosyvoice3_packed_streaming_optimized_standard.yaml

@@ -1,6 +1,8 @@
 # Opt-in single-Hopper streaming throughput profile: AR32 / codec32, Flow10.
 # Use --hf-overrides '{"cosyvoice3_sampling_mode": "standard"}' and stream=true.
 # F0 and HiFT stay FP32; only deterministic HiFT decode is graphed.
+# HiFT graphs capture on the third use of each exact shape, adding latency then.
+# The codec graph pool is not capped by gpu_memory_utilization; leave memory headroom.
 base_config: cosyvoice3_packed_streaming.yaml
 stages:
   - stage_id: 0